AFC Wimbledon boss Neal Ardley revealed Aaron Morris was unable to turn a move to League One down after he signed for Gillingham.
The 24-year-old defender, who made 17 appearances for the Dons last season, signed a two-year contract at Priestfield on Thursday after rejecting a new deal at Kingsmeadow.
"Unfortunately, Aaron was offered a very good deal by Gillingham, which shows how well he did with us last season," boss Ardley told the club's official website.
"We offered him the best deal possible that we could, but the lure of League One football was too strong.
"We wish Aaron all the best for the future and we would certainly welcome him back at Wimbledon."